awk '
BEGIN { FS = OFS = "\t"                                                        # Setting Field seperator and Output field seprator as tab
        fields[++nf] = 2                                                           # Creating an array named fields whose index is nf (which has values 1, 2 up to 3) and value is 2, 3 and 4
        fields[++nf] = 3                                                           # Assigning 2nd element as value 3 whose index is 2
        fields[++nf] = 4                                                           # Assigning 3rd element to array fields whose index is 3
}
FNR == 1 {                                                                          # This condition will be TRUE whenever it reads a new file
        f++                                                                             # increasing variable f's value by 1
}
f <= nf {l[f, $1] = $2                                                            # Checking condition here where variable f is less than and equal to variable nf's value, making array named l whose index is variable f and $1, setting it's value to $2, eg. l(1, 1)=a b
        next                                                                           # skipping other actions
}
{       for(i = nf; i > 0; i--) {                                                  # intilizing for loop from variable nf's value to 0
                n = split($fields[i], sf, " ")                                     # creating an array named sf whose seperator is space and taking it's count to variable n 
                af = OFS                                                             # setting a variable named af's value to OFS(Output field seprator)
                for(j = 1; j <= n; j++)                                          # intilizing a for loop whcih will run till variable j's value is equal to n's value
                        af = af l[i, sf[j]] ((j < n) ? " " : "")                  # setting value of af here eg. (af = af l(3, sf(1)) " ") which is actually [af=af 10 ] then (af = af l(3, sf(2)) " ") which is actually [af=af 10 20]
                $fields[i] = $fields[i] af                                        # Setting individual field's value in line by fields array 
        }
}         
1' Lookup2 Lookup3 Lookup4 file                                             # 1 means allow defualt action which is print here, filenames are given as input