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.

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

$\mathrm{true}$

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

$\mathrm{false}$