The type(expr, '`in`') function checks for expressions that are formed using the infix operator in. For more information about the in operator, see in.

$\mathrm{type}\left(a\mathbf{in}b\,'\mathrm{`in`}'\right)$

$\mathrm{true}$

$\mathrm{type}\left(a\mathbf{in}b\Rightarrow a\mathbf{in}c\,'\mathrm{`in`}'\right)$

$\mathrm{false}$