∑ℓ=0∞(hn⁡(qℓ;q)⁢hm⁡(qℓ;q)+hn⁡(-qℓ;q)⁢hm⁡(-qℓ;q))⁢(qℓ+1,-qℓ+1;q)∞⁢qℓ=(q;q)n⁢(q,-1,-q;q)∞⁢qn⁢(n-1)/2⁢δn,m.