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proc C s {expr ([regsub -all (.)(.) [string replra $s 7 70 0]6]0 {-3*\1-\2}])%10==[string in $s 7]}
Try it online!Try it online!
Will golf it more later!
proc C s {expr ([regsub -all (.)(.) [string repl $s 7 7 0] {-3*\1-\2}])%10==[string in $s 7]}
Try it online!
proc C s {expr ([regsub -all (.)(.) [string ra $s 0 6]0 {-3*\1-\2}])%10==[string in $s 7]}
