$${p + p \rightarrow \mathrm{D} + e^− + \nu^*_e + ...\\ \mathrm{D} + p \rightarrow \mathrm{^3 He} + ...\\ \mathrm{^3 He} + \mathrm{^3 He} \rightarrow \mathrm{^4 He} + p + p + ...}$$