Changes

* Show that <math>\lnot (p \Leftrightarrow q)</math> is equivalent to <math>(\lnot q) \Leftrightarrow p.</math>

* Show that <math>\lnot (p \Leftrightarrow q)</math> is equivalent to <math>(\lnot q) \Leftrightarrow p.</math>

We can translate this into logical graphs by supposing that we have to express everything in terms of negation and conjunction, using parentheses for negation and simple concatenation for conjunction, thus:

We can translate this into logical graphs by supposing that we have to express everything in terms of negation and conjunction, using parentheses for negation and simple concatenation for conjunction.  In this way of assigning logical meaning to graphical forms &mdash; for historical reasons called the "existential interpretation" of logical graphs &mdash; basic logical operations are given the following expressions:

The negation <math>\lnot x</math> is written <math>(x).\!</math>

The negation <math>\lnot x</math> is written <math>(x).\!</math>

And so on.

And so on.

The disjunction <math>x \lor y</math> is written <math>((x)(y)).\!</math>

The disjunction <math>x \lor y</math> is written <math>((x)(y)).\!</math>