| http://www.w3.org/ns/prov#value | - If now $a+b+ab=0$, the term $b(1+a+a^2)=b+ab+a^2b=-a + a^2b=a(ab-1)$ so we have $a(ab-1)=a\sqrt{a^2+b^2+1}$ and if $a\neq 0$ we can cancel and square to obtain $$(ab-1)^2=a^2+b^2+1$$ Now we can write $ab=-(a+b)$ so that the equation becomes $$a^2+b^2+1+(2ab+2a+2b)=a^2+b^2+1$$ The term in brackets is zero, so the equation is an identity and gives no additional constraint.
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