Can someone check my electrical engineering HWERK (Deals with KMAP)?

Question

Find SOP and POS of function (x1,x2,x3,x4) with E(0,2,8,9,10,15) + D(1,3,6,7)

After drawing my kmap i got....


SOP
F= x1'x2' + x2x3x4 + x1x2'x3 + x1x2'x3x4'


POS
F= (x2'+x3)(x2'+x3'+x4)(x1'+x2+x3'+x4)

Answer 1

WikiPedia on k-maps, with links to related:
http://en.wikipedia.org/wiki/Karnaugh_map

and

http://pico1.e.ft.fontys.nl/publicad.html
seems to have a download which might check the work.