Sum Nine Sudoku (321)

Instruction:

Apply classic sudoku rules. Adjacent cells containing numbers with the sum 9 are marked with a rhombus. Adjacent cells with no marking must not contain numbers with the sum 9.

Reference: WPF (1)

Examples:

WPF Sudoku GP 2017 - Round 6 (7)

Parent puzzle:
Neighbor Sums Sudoku

Child puzzles:
Diagonal Sum is Nine Sudoku

Related puzzles:
Sum 100 Sudoku