Packages\com.unity.uiwidgets\Runtime\engine\input_utils.cs(3,19): error CS0234: The type or namespace name 'EventSystems' does not exist in the namespace 'UnityEngine' (are you missing an assembly reference?)
Packages\com.unity.uiwidgets\Runtime\engine\UIWidgetsPanel.cs(11,30): error CS0234: The type or namespace name 'UI' does not exist in the namespace 'UnityEngine' (are you missing an assembly reference?)
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Unity2019.2.21f1
Packages\com.unity.uiwidgets\Runtime\engine\input_utils.cs(3,19): error CS0234: The type or namespace name 'EventSystems' does not exist in the namespace 'UnityEngine' (are you missing an assembly reference?) Packages\com.unity.uiwidgets\Runtime\engine\UIWidgetsPanel.cs(11,30): error CS0234: The type or namespace name 'UI' does not exist in the namespace 'UnityEngine' (are you missing an assembly reference?) ………………………… Unity2019.2.21f1