What does the symbol ⌒ mean?

Question

I have come across the following notation when summing over the orthogonal projections of an arbitrary base $n$ in the Hilbert space with $p_{i}, p_j$ being the probability finding the quantum state $\Psi_i, \Psi_j$

What does this ⌒ symbol mean?

Edit:

This is part of the following exercise

Answer 1

Now that I see the full context, I think I see what's happening:

There's an ongoing calculation, and the second equals sign is part of that ongoing calculation (that is, the thing to its right is equal to the thing on the previous line).

Left of it there is the completeness relation $$\sum_n \lvert n\rangle\langle n\rvert = \large{\unicode{0x1d7d9}}$$ where the double-struck $1$ () denotes the identity operator.

The arc is meant not as a mathematical symbol, but as a connecting line from that relation to the equals sign, to signify that the relation was used to establish that equality.