diff --git a/mapytex/calculus/core/str2.py b/mapytex/calculus/core/str2.py
index 0024d06..0630db0 100644
--- a/mapytex/calculus/core/str2.py
+++ b/mapytex/calculus/core/str2.py
@@ -11,7 +11,7 @@ Converting a string with coroutines
 """
 
 from functools import partial
-from decimal import Decimal
+from decimal import Decimal, InvalidOperation
 from .coroutine import *
 from .operator import is_operator
 from .MO import moify
@@ -420,13 +420,13 @@ def lookforNumbers(target):
     ...    str2list.send(i)
     Traceback (most recent call last):
         ...
-    mapytex.calculus.core.str2.ParsingError: Can't build a number with 2 dots (current is 12.3)
+    mapytex.calculus.core.str2.ParsingError: Can't build decimal with '12.3'
     >>> str2list = lookforNumbers(list_sink)
     >>> for i in ".34*67":
     ...    a = str2list.send(i)
     Traceback (most recent call last):
         ...
-    mapytex.calculus.core.str2.ParsingError: Can't build a number starting with a dot
+    mapytex.calculus.core.str2.ParsingError: Can't build decimal with ''
 
     >>> str2list = lookforNumbers(list_sink)
     >>> for i in "12-34":
@@ -468,31 +468,58 @@ def lookforNumbers(target):
                     int(tok)
                 except ValueError:
                     if tok == '.':
-                        if "." in current:
-                            raise ParsingError(f"Can't build a number with 2 dots (current is {current})")
-                        elif not current:
-                            raise ParsingError(f"Can't build a number starting with a dot")
-                        else:
+                        if current.replace("-", "", 1).isdigit():
                             current += tok
+                        else:
+                            raise ParsingError(f"Can't build decimal with '{current}'")
                     elif tok == '-':
-                        if current:
-                            target_.send(typifiy_numbers(current))
-                            target_.send('+')
-                        current = tok
-                    else:
-                        if current == '-':
+                        if current == "":
+                            current = tok
+                        elif current == ("("):
                             target_.send(current)
-                            current = ""
-                        elif current:
-                            target_.send(typifiy_numbers(current))
-                            current = ""
-                        target_.send(tok)
+                            current = "-"
+                        elif is_operator(current):
+                            if current == "-":
+                                current = "+"
+                            else:
+                                target_.send(current)
+                                current = "-"
+                        else:
+                            try:
+                                target_.send(typifiy_numbers(current))
+                            except InvalidOperation:
+                                target_.send(current)
+                            target_.send('+')
+                            current = tok
+                    else:
+                        if current == "":
+                            current = tok
+                        elif is_operator(current) and is_operator(tok):
+                            raise ParsingError(f"Can't parse with 2 operators next to each other")
+                        else:
+                            try:
+                                target_.send(typifiy_numbers(current))
+                            except InvalidOperation:
+                                target_.send(current)
+                            current = tok
                 else:
-                    current += tok
+                    if current == "":
+                        current = tok
+                    elif current == "-":
+                        current += tok
+                    elif current.replace(".", "", 1).replace("-", "", 1).isdigit():
+                        # make sure no double dotted number can't reach this place!
+                        current += tok
+                    else:
+                        target_.send(current)
+                        current = tok
 
     except STOOOP as err:
         if current:
-            target_.send(typifiy_numbers(current))
+            try:
+                target_.send(typifiy_numbers(current))
+            except InvalidOperation:
+                target_.send(current)
         yield target_.throw(err)
 
 def typifiy_numbers(number):
@@ -681,6 +708,14 @@ def str2(sink, convert_to_mo=True):
      > -
      | > None
      | > a
+
+    >>> exp = "a - 3"
+    >>> t = str2tree(exp)
+    >>> print(t)
+    +
+     > a
+     > -3
+
     >>> exp = "1-(3+4)"
     >>> t = str2tree(exp)
     >>> print(t)
diff --git a/mapytex/calculus/core/tree.py b/mapytex/calculus/core/tree.py
index e72f489..5a4f4d9 100644
--- a/mapytex/calculus/core/tree.py
+++ b/mapytex/calculus/core/tree.py
@@ -218,7 +218,7 @@ class Tree():
         >>> Tree.from_any_tree(t)
         Traceback (most recent call last):
             ...
-        TypeError: Tree can't have empty node or leaf
+        TypeError: Tree can't have empty node or leaf. Got node = * and right_value = None
         >>> t = MutableTree("-", None, 1)
         >>> print(t)
         -
@@ -243,7 +243,7 @@ class Tree():
 
         if node is None or \
                 right_value is None:
-                    raise TypeError("Tree can't have empty node or leaf")
+                    raise TypeError(f"Tree can't have empty node or leaf. Got node = {node} and right_value = {right_value}")
 
         try:
             left_value.IMLEAF