Poincaré 1895: loops at basepoint up to homotopy form group under concatenation. Functorial. Van-Kampen theorem (cross-listed L0). Examples π₁(S^1)=Z, π₁(S^2)=0. Cross-listed L0 fundamental-group-cross.
Poincaré 1895: loops at basepoint up to homotopy form group under concatenation. Functorial. Van-Kampen theorem (cross-listed L0). Examples π₁(S^1)=Z, π₁(S^2)=0. Cross-listed L0 fundamental-group-cross.