plotting a function of three variables



>From Valerij Pipin, Fri Aug 02, at 20:12:
 (...) 
 .If you have the function of three vars it could be visualized in 4 dim space or you might look at section
 .in 3D by plotting the sequence of graphs ff(x,y,{t=1...}).


i feel embaressed with 4-d real spaces, i prefer to look at sections... so 
how to plot f(x,y,t) at t=1.3 ? 

thank you

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Paolo Pumilia