86. Rewrite the following statement in the form “p if and only if q”.
r : If a quadrilateral is equiangular, then it is a rectangle and if a quadrilateral is a rectangle, then it is equiangular.

Write the component statements of it and use them to check whether the compound statement is true or not.
t : You are wet when it rains or you are in a river.

Check the validity of the following statement.
“Square of an integer is positive or negative”.

Show that the statement “The integer n is even if and only if n² is even’ is true.