standard   ← ∊∘(⌊\¨⊢⊂⍳∘≢)∘(1,2≠/⊢)∘(1⌷[2]⊢),⊢
modified   ← ∊∘(⌈\∘⌽¨⊢⊂⍳∘≢)∘(1,2≠/⊢)∘(1⌷[2]⊢),⊢
dense      ← (+\1,2≠/1⌷[2]⊢),⊢
ordinal    ← ⍳∘≢,⊢
fractional ← ∊∘((≢(/∘⊢)+/÷≢)¨⊢⊂⍳∘≢)∘(1,2≠/⊢)∘(1⌷[2]⊢),⊢