\hspace{n}

inserts a space of n pixels
Ex.: $$f(x)\hspace{6}=\hspace{6}0$$ gives $f(x)\hspace{6}=\hspace{6}0$
can be combined with the preceding command \unitlength{m}(default: m=1px) , which defines the applied unit
Ex.: $$\unitlength{20}a\hspace{2}b$$ gives $\unitlength{20}a\hspace{2}b$ , i.e. a space of 20x2=40px