For all n, j > 0: (Bj is n-connected.
Indeed any convex set (including ∅) is n-connected.)
For all n, j > 0: Sj is n-connected just if n ≠ j+1.
“path connected” is 1-connected.
simply connected is (1-connected and 2-connected)
Some sets and their connectivity: The nth entry on the right (n>0) is whether the body described below is n-connected:
S0 | F T T T … |
S1 | T F T T … |
S2 | T T F T … |
Bn | T T T T … |
T2: Torus | T F T T … |
ST2 = 3D volume bounded by T2: Torus | T F T T … |
Q = ST2 omitting a small solid void: | T F F T … |
Two disjoint copies of B2 | F T T T … |
Two disjoint copies of ST2 | F F T T … |
Two disjoint copies of S2 | F T F T … |
Two disjoint copies of Q. | F F F T … |
If sets P' and Q' are base families (they each serve as a base for topologies P and Q respectively) then P'×Q' is a base family which serves as a base for R the product topology for P and Q. I think that for each positive integer n, R is n-connected just if both P' and Q' are both n-connected. I think this goes for infinite products too.
It seems the definition goes over smoothly to ω-connected by reasoning about Hilbert space over the reals and the unit ball there. For Hilbert space we must use balls or simplexes, not cubes.