[expr.ass]/1:

In all cases, the assignment is sequenced after the value
computation of the right and left operands, and before the value computation of the assignment expression.
The right operand is sequenced before the left operand

[intro.execution]/15:

i = v[i++]; // the behavior is undefined
i = 7, i++, i++; // i becomes 9
i = i++ + 1; // the behavior is undefined
i = i + 1; // the value of i is incremented

With the assignment being sequenced after the value
computation of the right and left operands, why is i = v[i++] and i = i++ + 1 undefined behavior?