Concatenate parameters and string

[Benalish]

Hello there. This code should report who cast the buff, which buff cast, and who received it

local f = CreateFrame("Frame")
f:RegisterEvent("COMBAT_LOG_EVENT_UNFILTERED")
f:SetScript("OnEvent", function(self, event, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9, arg10, 
                                              arg11, arg12, arg13)
    if (event == "COMBAT_LOG_EVENT_UNFILTERED") then 
        if (arg2 == "SPELL_AURA_APPLIED") then --do stuffs
                end
    end
end)

What exactly do I have to write in order to get a sentence in the form "arg4 cast arg10 on arg7"?