let x1, x2, y1, y2 be set ; :: thesis: [:{x1,x2},{y1,y2}:] = {[x1,y1],[x1,y2],[x2,y1],[x2,y2]}
thus [:{x1,x2},{y1,y2}:] = [:{x1},{y1,y2}:] \/ [:{x2},{y1,y2}:] by ZFMISC_1:132
.= {[x1,y1],[x1,y2]} \/ [:{x2},{y1,y2}:] by ZFMISC_1:36
.= {[x1,y1],[x1,y2]} \/ {[x2,y1],[x2,y2]} by ZFMISC_1:36
.= {[x1,y1],[x1,y2],[x2,y1],[x2,y2]} by ENUMSET1:45 ; :: thesis: verum