[Right triangle ⏵ may be expanded, down triangle ⏷ to close. Button = tree pop-up. × = close pop-up.]

Terminal: run. Derivation Graphs: (left-to-right) compact / full; (top-down) full / compact.

Help: blue = parse inside. Abbr.: WS: Workspace; Initial WS: initial heads for Merge after LEX lookup.

WS n, n = 1,2,... for intermediate stages after Initial WS. Final WS: when WS items converge on a single SO.
Bracketing: {...} (Merge). {...} (FormSet). At Spellout, {...} indicates free word order. [word] indicates word is optionally present.
Head Hd_{selection/features}, e.g. p_θ = predicate head p that seeks a θ-relevant (θR) IA from the WS. p_θ is a θ-seeker (θS).
v_see:θ:pst = head v has complement see, a θR EA from the WS and TNS. v is also a θS.
INFL seeks θR from its complement (not the WS).
Complementizer C comes in different flavors wrt. Force, .e.g. declarative C, interrogative C_Q and relative clause head C_rel.
Features, e.g. TNS pres/pst or DET the/a (shorthand for a bundle of semantic features).
Note: φ-features, e.g. 1sg, appear only at Spellout. Some words do not project, turn into features, e.g. determiners.

Words: who met Bill

Initial WS 1: Bill meet_θ v_meet:_θ:_pst INFL_v who

WS 1: {meet_θ, Bill} v_meet:_θ:_pst INFL_v who

WS 2: {v_meet:_θ:_pst, {meet_θ, Bill}} INFL_v who

WS 3: {who, {v_meet:_θ:_pst, {meet_θ, Bill}}} INFL_v

WS 4: {INFL_v, {who, {v_meet:_θ:_pst, {meet_θ, Bill}}}}

Final WS: {C_Q:_left(who), {INFL_v, {who, {v_meet:_θ:_pst, {meet_θ, Bill}}}}}

INT/EXT: {C_Q:_left(who), {INFL_v, {who, {v_meet:_θ:_pst, {meet_θ, Bill}}}}}

EXT: who →→ 3sg pst meet Bill

Spellout: who 3sg pst meet Bill

Spellout: who met Bill

Parse found: who →→ 3sg pst meet Bill

WS 1: {meet_θ, who} Bill v_meet:_θ:_pst INFL_v

WS 2: {v_meet:_θ:_pst:_box(who), {meet_θ, who}} Bill INFL_v

WS 3: {Bill, {v_meet:_θ:_pst:_box(who), {meet_θ, who}}} INFL_v

WS 4: {INFL_v, {Bill, {v_meet:_θ:_pst:_box(who), {meet_θ, who}}}}

Final WS: {C_Q:_left(who), {INFL_v, {Bill, {v_meet:_θ:_pst:_box(who), {meet_θ, who}}}}}

INT/EXT: {C_Q:_left(who), {INFL_v, {Bill, {v_meet:_θ:_pst:_box(who), {meet_θ, who}}}}}

EXT: who null pst meet →→ Bill 3sg pst meet

Spellout: who 3sg pst do Bill meet

Spellout: who did Bill meet

Blocked: inconsistent with input!

WS 1: {Bill, who} meet_θ v_meet:_θ:_pst INFL_v

WS 2: {meet_θ, {Bill, who}} v_meet:_θ:_pst INFL_v

WS 3: {v_meet:_θ:_pst:_box(who), {meet_θ, {Bill, who}}} INFL_v

WS 4: {{Bill, who}, {v_meet:_θ:_pst:_box(who), {meet_θ, {Bill, who}}}} INFL_v

WS 5: {INFL_v, {{Bill, who}, {v_meet:_θ:_pst:_box(who), {meet_θ, {Bill, who}}}}}

Initial WS 2: Bill meet_θ v_meet:_θ:_pst INFL_v C_rel:_who

WS 1: {meet_θ, Bill} v_meet:_θ:_pst INFL_v C_rel:_who

WS 2: {v_meet:_θ:_pst, {meet_θ, Bill}} INFL_v C_rel:_who