Logical expressions behave inconsistently/incorrectly

[latkin]

Encountered this via web usage, have not tried with a local client. Chrome 43.0.2357.124

Here is a minimal example of equivalent logical expressions behaving inconsistently:

Here is a slightly more complex example, showing logical expressions behaving very inconsistently. The final example looks to be completely wrong.

[sn6uv]

Thanks for reporting this.

This looks like a combination of two things to me. Equal is flattening its arguments when it shouldn't:

In[1]:= Hold[Equal[0, 0] == True] // FullForm
Out[1]= Hold[Equal[0, 0, True]]

expected

Hold[Equal[Equal[0, 0], True]]

The second one is a bug in the evaluation of the flattened arguments

In[2]:= Equal[0, 0, True]
Out[2]= 0 == 0 == True

expected

0 == True

The second example is similar,

In[3]:= Hold[(0 == 0) != (2 == 0)] // FullForm
Out[3]= Hold[Inequality[0, Equal, 0, Unequal, Equal[2, 0]]]

expected

Hold[Unequal[Equal[0, 0], Equal[2, 0]]]

which also evaluates incorrectly

In[4]:= Unequal[Equal[0, 0], Equal[2, 0]]
Out[4]= True != False

expected

False

[sn6uv]

The parsing issue actually affects all flat operators, e.g. Plus[a, b] + c parses as Plus[a, b, c] which is wrong.