Two quantum particles can be described by one joint amplitude table. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
A pair has one joint amplitude table
The nonzero joint amplitudes sit on the zero-zero and one-one same-outcome cells. Each has probability 1/2.
Psame cells=21
Only the same-outcome cells are populated
The joint table is read cell by cell before any single correlation sentence is made.