let X be non empty disjoint_with_NAT set ; :: thesis: for p being FinSequence of (FreeUnivAlgNSG (ECIW-signature,X)) st 2 -tree p is Element of (FreeUnivAlgNSG (ECIW-signature,X)) holds
ex I1, I2 being Element of (FreeUnivAlgNSG (ECIW-signature,X)) st p = <*I1,I2*>
set S = ECIW-signature ;
set G = DTConUA (ECIW-signature,X);
set A = FreeUnivAlgNSG (ECIW-signature,X);
let p be FinSequence of (FreeUnivAlgNSG (ECIW-signature,X)); :: thesis: ( 2 -tree p is Element of (FreeUnivAlgNSG (ECIW-signature,X)) implies ex I1, I2 being Element of (FreeUnivAlgNSG (ECIW-signature,X)) st p = <*I1,I2*> )
assume 2 -tree p is Element of (FreeUnivAlgNSG (ECIW-signature,X)) ; :: thesis: ex I1, I2 being Element of (FreeUnivAlgNSG (ECIW-signature,X)) st p = <*I1,I2*>
then reconsider I = 2 -tree p as Element of (FreeUnivAlgNSG (ECIW-signature,X)) ;

per cases ( ex x being Element of X st I = root-tree x or ex n being Nat ex p being FinSequence of (FreeUnivAlgNSG (ECIW-signature,X)) st
( n in Seg 4 & I = n -tree p & len p = ECIW-signature . n ) ) by Th56;

suppose ex x being Element of X st I = root-tree x ; :: thesis: ex I1, I2 being Element of (FreeUnivAlgNSG (ECIW-signature,X)) st p = <*I1,I2*>

then consider x being Element of X such that
A1: 2 -tree p = root-tree x ;
2 -tree p = x -tree (<*> (TS (DTConUA (ECIW-signature,X)))) by A1, TREES_4:20;
then 2 = x by TREES_4:15;
then X meets NAT by XBOOLE_0:3;
hence ex I1, I2 being Element of (FreeUnivAlgNSG (ECIW-signature,X)) st p = <*I1,I2*> by FREEALG:def 1; :: thesis: verum

end;

suppose ex n being Nat ex p being FinSequence of (FreeUnivAlgNSG (ECIW-signature,X)) st
( n in Seg 4 & I = n -tree p & len p = ECIW-signature . n ) ; :: thesis: ex I1, I2 being Element of (FreeUnivAlgNSG (ECIW-signature,X)) st p = <*I1,I2*>

then consider n being Nat, q being FinSequence of (FreeUnivAlgNSG (ECIW-signature,X)) such that
n in Seg 4 and
A2: I = n -tree q and
A3: len q = ECIW-signature . n ;
A4: n = 2 by A2, TREES_4:15;
A5: q = p by A2, TREES_4:15;
then p = <*(p . 1),(p . 2)*> by A3, A4, Th54, FINSEQ_1:44;
then rng p = {(p . 1),(p . 2)} by FINSEQ_2:127;
then reconsider I1 = p . 1, I2 = p . 2 as Element of (FreeUnivAlgNSG (ECIW-signature,X)) by ZFMISC_1:32;
take I1 ; :: thesis: ex I2 being Element of (FreeUnivAlgNSG (ECIW-signature,X)) st p = <*I1,I2*>
take I2 ; :: thesis: p = <*I1,I2*>
thus p = <*I1,I2*> by A3, A4, A5, Th54, FINSEQ_1:44; :: thesis: verum

end;

end;