שינויים

====פתרון====

<math>(x,y)\in (A\times B)\cap (C\times D) \iff </math>

<math>(x,y)\in A\times B \land (x,y)\in C\times D \iff</math>

<math>(x\in A \and y\in B) \and (x\in C\and y\in D) \iff</math>

<math>(x\in A\and x\in C) \and (y\in B\and y\in D) \iff</math>

<math>(x,y)\in (A\cap C)\times (B\cap D)</math>