"Binary" operators are really Infix operators

That is, they can take more than two arguments. The operator
appears in betweek all operands.

mathics/core/builtin.py

@@ -1133,7 +1133,8 @@ def __init__(self, *args, **kwargs):
 
 class BinaryOperator(Operator):
     """
-    Class for Builtin Binary Operators, e.g. Plus (+)
+    Class for Builtin Infix Operators (which includes Binary
+    operators), e.g. Plus (+).
     """
 
     # Note: grouping must be Python string, not a Symbol.