We should know that an expression in POS form is always easier to be realized by NOR gates.
Given is the SOP ∑m(0,2,6,10,14) so we should convert it to POS.
Hence piM(1,3,4,5,7,8,9,11,12,13,15) [I couldn't find the "pi" symbol :P]
So the expression is D'.(B'+C).(A'+C)
Now we have to convert this expression in such a way that we can realize it with NOR
( ( D'.(B'+C).(A'+C) )' )' = ( (D')' + (B'+C)' + (A'+C)' )' = (D + BC' + AC' )'
= (D + C'(A+B) )' = ( D + ( ( C'(A+B) )' )' )' = (D + ( (C')' + (A+B)' )' )'
= (D + ( C + (A+B)' )' )'
X=(A+B)' --> 1 NOR
Y=(C+ X)' --> 1 NOR
(D+Y)' --> 1 NOR