The call type(expr, boolean_function) returns true if expr is of type boolean_function.

The type boolean_function is defined as an object of type function whose zeroth operand is one of the global symbols And, Or, Not, Xor, or Implies.

Note that this type only checks the top level and does not perform any type checking on subexpressions.

$\mathrm{type}\left(x\mathbf{and}y\,\mathrm{boolean\_function}\right)$

$\mathrm{false}$

$\mathrm{type}\left(\mathrm{And}\left(x\,y\,\mathrm{Or}\left(a\,b\right)\right)\,\mathrm{boolean\_function}\right)$

$\mathrm{true}$

$\mathrm{type}\left(x\Rightarrow y⊻z\,\mathrm{boolean\_function}\right)$

$\mathrm{true}$