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

Unaccusative verb arrive (cf. Spanish llegar here):
Variants: A train arrived / *A train arrive / There arrived a train / There is arriving a train / A train has arrived
More complex: Has a train arrived? / Did a train arrive?

g [a,train,arrived] [a,train,arrived] [a,train,has,arrived] [a,train,has,arrived] [a,train,arrived]->[a,train,has,arrived] [there,arrived,a,train] [there,arrived,a,train] [a,train,arrived]->[there,arrived,a,train] [has,a,train,arrived] [has,a,train,arrived] [a,train,has,arrived]->[has,a,train,arrived] [has,a,train,arrived]->[a,train,has,arrived] [a,train,arrive] [a,train,arrive] [did,a,train,arrive] [did,a,train,arrive] [a,train,arrive]->[did,a,train,arrive] [there,is,arriving,a,train] [there,is,arriving,a,train] [a,train,arrives] [a,train,arrives] [a,train,arrives]->[a,train,arrived] [a,train,arrives]->[a,train,arrive] [there,arrived,a,train]->[there,is,arriving,a,train]

Help: blue = parse inside. Abbr.: WS: Workspace; Initial WS: initial heads for Merge after LEX lookup.
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Words: a train arrives
Initial WS 1: arriveθ varrive:pres INFLv:3sg traina 
WS 1: {arriveθ, traina} varrive:pres INFLv:3sg 
WS 2: {varrive:pres, {arriveθ, traina}} INFLv:3sg 
WS 3: {INFLv:3sg, {varrive:pres, {arriveθ, traina}}} 
Final WS: {C, {INFLv:3sg, {varrive:pres, {arriveθ, traina}}}} 
INT/EXT: {C, {INFLv:3sg, {varrive:pres, {arriveθ, traina}}}}
EXT: a train 3sg pres arrive
Spellout: a train arrives
Parse found: a train 3sg pres arrive
EXT: there 3sg pres arrive a train
Spellout: there arrives a train
Blocked: inconsistent with input!