(This post is part of the Genuinely Approachable Sudoku (GAS) series.)
Philip brings another two-variation Sudoku with this Fortress (gray cells larger than surrounding white cells) and XVXV Pairs (5/10/15 edge sums) challenge. It should make you go “?” for sure, but “Will It GAS?”

PDF

or solve online (using SudokuPad)

Theme: Will It GAS?

Author/Opus: This is the 51st puzzle from Philip Newman, part of the Genuinely Approachable Sudoku (GAS) team.

Rules: Standard Sudoku rules (Insert a number from 1 to 9 into each cell so that no number repeats in any row, column, or bold region). A number in a gray cell must be larger than any number in an adjacent white cell that shares an edge. (To assist solvers, this is shown like a greater than/less than shape in how the gray cells are drawn.) Also, whenever a V, X, or XV reflecting the numbers 5, 10, or 15 in Roman numerals, is placed on the edge between cells, the numbers in the two adjacent cells must sum to exactly 5, 10, or 15. (Pairs of cells without a V, X or XV can have any sum value.)

GAS Time Standards (highlight to view): Two party hats (🎩🥳): 7:30; One party hat (🥳): 16:00. All other solvers earn a 🦕: Protective Punatitan.

Thomas Hits the GAS (highlight to view): 4:16, with SudokuPad replay file shared as a download for now (requires loading via settings menu with improvements expected before people should use this regularly).

Solution: PDF; solving video with explanation to be added later from GAS team.

Note: Follow this link for other less common variations of Sudoku.

Note 2: Comments on the blog are great! For a more interactive discussion, please also consider using our Daily GAS discussion post on the GMPuzzles Discord. Not a member of the Discord? Click this link for basic access.