I want to write the following statement in only maths notation without any words:
$$\sum^n_{r=1}r=0.5n(n+1)$$ is true for all positive integers n.
This is what I have got so far.
$$\sum^n_{r=1}r=0.5n(n+1)$$ is true $\forall n\in \mathbb{N}_1 $
Is there any maths symbols to say 'is true'?