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Fate Core — active opposition to an overcome action

R13 · Advanced · Scoped component

Question and scope

A Fate Core overcome action faces active opposition from another character with equal skill. Compare their independent 4dF rolls. Predict whether strict wins and strict losses are equally likely, and whether a tie is failure.

Source sections are linked under Rules below; primary-source review is recorded in the release dossier. Independent human and browser/usability review are separate gates.

Inputs and model limits

Equal skill on two independent 4dF rolls. To compare unequal skills add each supplied skill to its roll. No invocation/cost decision is modelled.

Complete runnable model

joint_classify(left, right, scale, function) calls the function with one value from each distribution. Subtracting the actual callback values gives their shared margin. For an overcome action, a tie attains the goal at a minor cost; a positive margin succeeds, and margin 3+ succeeds with style.

f = die_faces([-1, 0, 1])
roll = f + f + f + f
bands = scale().step("Below opposition").step("Tie: minor cost").step("Succeed").step("With style")
def compare(left, right):
    margin = left - right
    if margin < 0:
        return "Below opposition"
    if margin == 0:
        return "Tie: minor cost"
    if margin >= 3:
        return "With style"
    return "Succeed"
result = joint_classify(roll, roll, bands, compare)
output("Equal-skill overcome action", result)
output("Tie", result.pmf("Tie: minor cost"))
output("Strictly beat opposition", result.p_at_least("Succeed"))

Equal-skill overcome action · Outcomes

Tie · Prob

Strictly beat opposition · Prob

Reading the report and independent checks

Tie probability is 1107/6561. Strictly beating opposition is 2727/6561, equal to falling below it by symmetry. The denominator is 81×81 sign sequences. A below-opposition result can still lead to success at a serious cost by the game’s rules; this report does not choose that option.

Safe changes

Add +1 to the first roll only. Strict wins increase; symmetry between win and loss is broken. Ties must still be reported under the same convention.

Composition and boundary checks

For two opposed d6, build lose/tie/win categories. Answer: 15/36,6/36,15/36. Checkpoint: name the tie rule and explain why both dice are independent, even if both arguments reference one distribution variable.

Do not combine separate marginal reports and assume they preserve the same rolled faces. When an event depends on several properties of one roll, keep those properties together inside a single classifier or pool callback.

Rules

Fate Core SRD, dice and the ladder. Four independent Fate dice; their faces are equally weighted −1, 0, +1. Other Fate/Fudge variants are not implied. Four Actions: Overcome. Outcome classification only; no invocations, active-defender resources, or choice of serious cost.

Related learning

Lesson L24 explains the modelling idea step by step. Cookbook index offers both game and mechanic views of these same recipes.

Content ID: R13 · Review status: pilot

Prerequisites: L24