DecodeXOR←{
⍝ ⍺: initial
⍝ ⍵: encoded sequence
⍝ ←: original array that produced ⍵
⍝    ⍵ ← 2{2⊥≠/2⊥⍣¯1⊢⍵}/original
     0∊⍴⍵:⍺
     nxt←2⊥≠/2⊥⍣¯1⊢⍺,⊃⍵
     ⍺,nxt ∇ 1↓⍵

⍝ Examples:
⍝       1 DecodeXOR 1 2 3
⍝ 1 0 2 1
⍝       4 DecodeXOR 6 2 7 3
⍝ 4 2 0 7 4
 }