§ Wedge Sum and Smash Product
I sometimes forget which is which. I now remember this as folows:
- First, these work on based spaces so we always need to think of based points.
- Wedge is a sum, so it's going to be some type of union. It needs to identify things, so it better be A∪B/∼ where ∼ identifies based points.
- Smash is a product, so it's going to be some type of product. It needs to identify things, so it better be A×B/∼, where ∼ crushes together anything that has a based point. So (∗,a),(a,∗),(∗,∗) are all crushed.
- If we don't remember the "sum" and "product" bit, and only remember "wedge" and "smash", then "wedge" starts with a "w" which looks like
\/
so it should be a union.