I think it's an incorrect statement. A square is a rhombus (cf, post #4) "Every rhombus is a parallelogram, and a rhombus with right angles is a square.[SUP][1][/SUP][SUP][2]"
[/SUP]http://en.wikipedia.org/wiki/Rhombus
A square is a rectangle, a quadrangle, and a rhombus.
A square quadrangle IS a rhomboid rectangle. Example - a square.
In fact all square quadrangles are rhomboid rectangles. In that case, "All quadrangles that are squares are rectangles that are rhombuses."
Breaking the original down in another way: A: "No quadrangle that is a square is a rectangle that is a rhombus."
B: A quadrangle that is a square is a square. Therefore, the statement becomes:
C: "No square is a rectangle that is a rhombus
D: But a rectangle that is a rhombus is a rhombus. Therefore the statement becomes:
E: No square is a rhombus.
F: But all squares are rhombuses (as Wiki tells us).
G: If all squares are rhombuses, then "All quadrangles that are squares are rectangles that are rhombuses.
Have I missed something obvious?