Cardinality

• How to Prove Two Nondegenerate Closed Intervals Have Equal Cardinality
  A linear bijection proves bounded nondegenerate closed intervals have equal cardinality; unbounded intervals with more than one point do too.
• Are the Positive Multiples of 17 and 11 in Bijection?
  The positive multiples of 17 and 11 are in bijection: match 17k with 11k for each positive integer k, and verify the map is one-to-one and onto.
• How Do You Find the Cardinality of a Set Containing Sets?
  To find the cardinality of a set containing sets, count its distinct outer elements; do not add the numbers of elements inside those sets.