As others remark, there are no standard Compose rules in X for π, so if you want to use Compose to make the π symbol, you could define it yourself in a custom ~/.XCompose file (note the capital C). An example is provided below. Note that you should start the file with include "%L" if you want to inherit the Compose definitions from your current locale.
You might need to restart your desktop environment for the changes to take effect.
Example
This example assumes you will want to type Compose key g followed by a greek letter mnemonic. For example:
- Compose key g p i for π
- Compose key g O h for Ω
- Compose key g o h for ω
- etc.
include "%L" <Multi_key> <l> <l> : "ℓ" U2113 # LITRE SYMBOL <Multi_key> <g> <A> <l> : "A" U0391 # GREEK CAPITAL LETTER ALPHA <Multi_key> <g> <a> <l> : "α" U03B1 # GREEK SMALL LETTER ALPHA <Multi_key> <g> <B> <e> : "B" U0392 # GREEK CAPITAL LETTER BETA <Multi_key> <g> <b> <e> : "β" U03B2 # GREEK SMALL LETTER BETA <Multi_key> <g> <G> <a> : "Γ" U0393 # GREEK CAPITAL LETTER GAMMA <Multi_key> <g> <g> <a> : "γ" U03B3 # GREEK SMALL LETTER GAMMA <Multi_key> <g> <D> <e> : "Δ" U0394 # GREEK CAPITAL LETTER DELTA <Multi_key> <g> <d> <e> : "δ" U03B4 # GREEK SMALL LETTER DELTA <Multi_key> <g> <E> <p> : "E" U0395 # GREEK CAPITAL LETTER EPSILON <Multi_key> <g> <e> <p> : "ϵ" U03B5 # GREEK SMALL LETTER EPSILON <Multi_key> <g> <Z> <e> : "Z" U0396 # GREEK CAPITAL LETTER ZETA <Multi_key> <g> <z> <e> : "ζ" U03B6 # GREEK SMALL LETTER ZETA <Multi_key> <g> <E> <t> : "H" U0397 # GREEK CAPITAL LETTER ETA <Multi_key> <g> <e> <t> : "η" U03B7 # GREEK SMALL LETTER ETA <Multi_key> <g> <T> <h> : "Θ" U0398 # GREEK CAPITAL LETTER THETA <Multi_key> <g> <t> <h> : "θ" U03B8 # GREEK SMALL LETTER THETA <Multi_key> <g> <I> <o> : "I" U0399 # GREEK CAPITAL LETTER IOTA <Multi_key> <g> <i> <o> : "ι" U03B9 # GREEK SMALL LETTER IOTA <Multi_key> <g> <K> <a> : "K" U039A # GREEK CAPITAL LETTER KAPPA <Multi_key> <g> <k> <a> : "κ" U03BA # GREEK SMALL LETTER KAPPA <Multi_key> <g> <L> <a> : "Λ" U039B # GREEK CAPITAL LETTER LAMBDA <Multi_key> <g> <l> <a> : "λ" U03BB # GREEK SMALL LETTER LAMBDA <Multi_key> <g> <M> <u> : "M" U039C # GREEK CAPITAL LETTER MU <Multi_key> <g> <m> <u> : "μ" U03BC # GREEK SMALL LETTER MU <Multi_key> <g> <N> <u> : "N" U039D # GREEK CAPITAL LETTER NU <Multi_key> <g> <n> <u> : "ν" U03BD # GREEK SMALL LETTER NU <Multi_key> <g> <X> <i> : "Ξ" U039E # GREEK CAPITAL LETTER XI <Multi_key> <g> <x> <i> : "ξ" U03BE # GREEK SMALL LETTER XI <Multi_key> <g> <O> <m> : "O" U039F # GREEK CAPITAL LETTER OMICRON <Multi_key> <g> <o> <m> : "o" U03BF # GREEK SMALL LETTER OMICRON <Multi_key> <g> <P> <i> : "Π" U03A0 # GREEK CAPITAL LETTER PI <Multi_key> <g> <p> <i> : "π" U03C0 # GREEK SMALL LETTER PI <Multi_key> <g> <R> <h> : "P" U03A1 # GREEK CAPITAL LETTER RHO <Multi_key> <g> <r> <h> : "ρ" U03C1 # GREEK SMALL LETTER RHO <Multi_key> <g> <S> <i> : "Σ" U03A3 # GREEK CAPITAL LETTER SIGMA <Multi_key> <g> <s> <i> : "σ" U03C3 # GREEK SMALL LETTER SIGMA <Multi_key> <g> <T> <a> : "T" U03A4 # GREEK CAPITAL LETTER TAU <Multi_key> <g> <t> <a> : "τ" U03C4 # GREEK SMALL LETTER TAU <Multi_key> <g> <U> <p> : "ϒ" U03A5 # GREEK CAPITAL LETTER UPSILON <Multi_key> <g> <u> <p> : "υ" U03C5 # GREEK SMALL LETTER UPSILON <Multi_key> <g> <P> <h> : "Φ" U03A6 # GREEK CAPITAL LETTER PHI <Multi_key> <g> <p> <h> : "ϕ" U03C6 # GREEK SMALL LETTER PHI <Multi_key> <g> <C> <h> : "X" U03A7 # GREEK CAPITAL LETTER CHI <Multi_key> <g> <c> <h> : "χ" U03C7 # GREEK SMALL LETTER CHI <Multi_key> <g> <P> <s> : "Ψ" U03A8 # GREEK CAPITAL LETTER PSI <Multi_key> <g> <p> <s> : "ψ" U03C8 # GREEK SMALL LETTER PSI <Multi_key> <g> <O> <h> : "Ω" U03A9 # GREEK CAPITAL LETTER OMEGA <Multi_key> <g> <o> <h> : "ω" U03C9 # GREEK SMALL LETTER OMEGA
