Expressions Simplifications Boolean Algebra

Expressions Simplifications Boolean Algebra
I started simplifying function and got to the detailed picture and wanted to know if I can reduce the above expressions, for example :

Y'.X'.Y = 0 ?
Y'.X'.Z.X = 0 ?

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Yes. Both disjunction and conjunction are commutative in a boolean algebra. Hence $$Y^\prime X^\prime Y = X^\prime YY^\prime=0$$ for instance.

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and YXY will be equal to XY ? because of YY=Y, and Y'Y'=Y' ? – Ofir Attia Apr 20 '13 at 13:03
Yes, exactly. ${}{}{}{}$ – Abel Apr 20 '13 at 13:04
Thank you, really helped me – Ofir Attia Apr 20 '13 at 13:05