f := (x,y,z) -> x*sin(y)+y*cos(z); `f(0,0,0)` = f(0,0,0); `f(1,Pi/2,Pi)` = f(1,Pi/2,Pi); `f(1,Pi,Pi/2)` = f(1,Pi,Pi/2); `diff(f(x,x,x),x)` = diff(f(x,x,x),x); collect(%,{sin(x),cos(x)}); `diff(f(y,y,0),y)` = diff(f(y,y,0),y);