A - B means A is the husband of B; A × B means A is the brother of B; A + B…

Concept: In a coded blood-relation puzzle, each symbol fixes one atomic relation between the two letters it joins (for example, A ÷ B always fixes B as A's father). A compound relation such as "maternal grandfather" must be built by chaining three atomic links in the correct order and direction: child, to that child's father, to the father's wife (the mother), to the mother's father.

Application: To show that U is the maternal grandfather of R, we need the chain R, to R's father, to that father's wife (R's mother), to the mother's father. Reading R + T - S ÷ U left to right does exactly this:

1. R + T fixes T as R's father, i.e. R is the son of T.

2. T - S fixes S as T's wife, so S is R's mother.

3. S ÷ U fixes U as S's father, i.e. U is the father of R's mother.

Cross-check: Drawing the family tree from the same three links independently confirms it — T and S are a married couple, R is their son (so S, not T, is R's mother), and U is S's father. Following the line up from R through R's mother S to her father U places U exactly two generations above R on the mother's side.

Result: U is the father of R's mother, which is precisely the maternal-grandfather relation. So R + T - S ÷ U is the expression that indicates U is the maternal grandfather of R.